In general, pneumatic tires for heavy load vehicles are used in a severe environment, and therefore a rubber composition which is excellent in durability has to be used for rubber members constituting the above pneumatic tires for heavy load vehicles, for example, an inner liner and a rubber layer brought into direct contact with the above inner liner.
In a pneumatic tire of a tubeless type for heavy load vehicles, a rubber which is excellent in an air impermeability has so far been desired for an inner liner, and a halogenated butyl rubber alone or a blend rubber of a halogenated butyl rubber with a diene rubber considering an adhesive property and rubber adjacent to an inner liner is usually used therefor.
However, sufficiently high adhesion after vulcanization is not obtained by a halogenated butyl rubber alone, and if puncturing and dragging are brought about, an inner liner is peeled off, so that a blend rubber of a halogenated butyl rubber and a diene rubber is used frequently at the sacrifice of an air impermeability in order to improve an adhesive force.
Known as conventional rubber compositions for inner liners of tires, rubber layers brought into direct contact with inner liners, and the like are:    1) a rubber composition for an inner liner of a tire prepared by blending 100 parts by weight of a diene rubber containing 50% by weight or more of a halogenated butyl rubber with 0.5 to 4 parts by weight of polyalkylene glycol having a molecular weight of 106 to 500 and 0 to 0.3 part by weight of sulfur as a rubber composition for an inner liner of a tire, which makes it hard to bring about a compression set even under a high temperature and a high pressure in running while inhibiting a change in a modulus and maintaining a heat aging resistance (refer to, for example, patent document 1),    2) a tire for heavy load vehicles in which a rubber composition prepared by blending 100 parts by mass of a rubber component containing total 50 to 98% by mass of at least one of a natural rubber and a polyisoprene rubber and 2.0 to 15.0% by mass of a trans-polybutadiene rubber with 40 to 80 parts by mass of carbon black having a N2SA of 20 to 70 m2/g and a DBP oil absorption of 60 to 130 ml/100 g, and 3 to 14 parts by mass of sulfur, or a rubber composition prepared by blending 100 parts by mass of a rubber component containing total 50 to 100% by mass of at least one of a natural rubber and a polyisoprene rubber with 40 to 80 parts by mass of carbon black having a N2SA of 20 to 70 m2/g and a DBP oil absorption of 60 to 130 ml/100 g, 3 to 14 parts by mass of sulfur, and 0.3 to 2.0 parts by mass of a heat-resistant cross-linking agent is applied to an interlayer rubber located between a carcass and an inner liner (refer to, for example, patent document 2 filed by the present applicants),    3) a heavy load bias tire in which a rubber composition prepared by blending 1 to 8 parts by weight of a non-reactive alkylphenol resin having a softening point of 60 to 115° C. and an acid value of 1 to 60 with 100 parts by weight of a rubber containing a diene rubber alone or a diene rubber and a halogenated butyl rubber which are used in combination in a range of 95/5 to 50/50, and further adding and blending 0.5 to 3 parts by weight of sulfur and an accelerator so that a ratio of the sulfur and the accelerator falls in a range of 5 or less is used as an inner liner adjacent member (refer to, for example, patent document 3 filed by the present applicants), and    4) a tire for large-sized vehicles in which a rubber composition comprising a rubber component containing a natural rubber or a diene rubber, and containing at least one of specific hydrazone compounds is used for a rubber layer brought into direct contact with an inner liner in order to enhance an adhesive power of a member adjacent to the above inner liner after thermally deteriorated (refer to, for example, patent document 4 filed by the present applicants).
However, the tires for heavy load vehicles, and the like disclosed in patent documents 1 to 4 described above involves a problem in terms of a still insufficient inhibition of a reduction in an elongation at break caused by heat aging of the rubber.
In particular, in the case of pneumatic tires for heavy load vehicles, specifically tires which are thermally affected to a large extent, though the tires have a thick tire gauge and generate a large amount of heat by rolling, an inner liner side is thermally affected to a large extent because of an insufficient exothermal effect. Accordingly, the existing situation is that a rubber adjacent to the inner liner is thermally aged by oxidative deterioration due to the influences of oxygen and heat permeated from an inner liner side and reduced in an elongation at break, whereby the rubber adjacent to the inner liner is liable to be cracked and that durability is intensely desired to be further enhanced.